This is a new one. It's sound like the iOS crashed or it got somehow erased. Do you have any backups of the device? You can try to connect it to iTunes in DFU Mode to do a full restore and see if you can start over. If you don't have any backups, your data will be gone.
Another side question, does his Apple ID and password work on other Apple sites, like iTunes or iCloud? If not, he may need to recover his Apple ID and update the password.
Try logging into iCloud.com on the computer to see if your Apple ID works. If not, like Khalil said, you'll want to reset the password at https://iforgot.apple.com/password/verify/appleid